Stacked gratings for optical emitters

A method, comprising:

• disposing a first set of layers of material on a substrate to form an emitter with an oxidation aperture,
• wherein the first set of layers includes a bottom distributed Bragg reflector (DBR) and a first subset of layers of a top DBR;
• patterning a surface of the first set of layers to form an etching pattern;
• etching the etching pattern to form a sub-surface periodic grating structure;
• and
• disposing a second set of layers of material onto the sub-surface periodic grating structure,
• wherein the second set of layers of material includes a second subset of layers of the top DBR forming a surface periodic grating structure,
• wherein the surface periodic grating structure has a selected period, depth, and fill factor,
• wherein the selected period, depth, and fill factor of the surface periodic grating structure are selected to achieve greater than a threshold level of optical field confinement in a transverse direction of an optical field emitted by the optical emitter, and
• wherein the sub-surface periodic grating structure comprises a plurality of portions having stacks and gaps of non-uniform width, wherein vertical alignment of high refractive index layers varies among the plurality of portions.

An optical element, comprising:

• an oxidation aperture;
• one or more distributed Bragg reflectors (DBRs) disposed on the oxidation aperture;
• and
• a stacked periodic grating structure formed between a first subset of layers of the one or more DBRs and a second subset of layers of the one or more DBRs,
• wherein the stacked periodic grating structure has a selected period, depth, and fill factor,
• wherein the selected period, depth, and fill factor of the stacked periodic grating structure are selected to achieve greater than a threshold level of optical field confinement in a transverse direction of an optical field emitted by the optical emitter, and
• wherein the stacked periodic grating structure comprises a plurality of portions having stacks and gaps of non-uniform width, wherein vertical alignment of high refractive index layers varies among the plurality of portions.